Halogen doped bi2te3-bi2se3-as2se3 thermoelectric composition



March 21, 1967 RUPPRECHT HALOGEN DOPED B Te -B' Se -A 3,310,493 1 3 56 THERMO-ELECTRIC COMPOSITION Filed May 2, 1963 United States Patent 3,310,493 HALOGEN DOPED Bi Te -Bi Se -As Se THERMO- ELECTRIC COMPOSITION Joachim Rupprecht, Nurnberg, Germany, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin-Siemcnsstadt, Germany, a corporation of Germany Filed May 2, 1963, Ser. No. 277,616

Claims priority, applicatiil ggrmanynlune 29, 1962,

4 Claims. cl. 252-62.3)

My invention relates to thermoelectric semiconductor devices and in a particular aspect to semiconductors for use as thermocouple legs in Peltier piles or batteries.

The thermocouples employed for electric cooling on the Peltier principle are composed of semiconductor components or legs which in each pair have n-type and p-type conductance respectively. The suitability of the semiconductor for such purposes is predicated upon exhibiting a high value of thermoelectric eifectivity (z) defined by:

in which T denotes the temperature of the cold junction. A good Peltier semiconductor, therefore, is not only supposed to have high effectivity at room temperature, but the eifectivity must also be as high as possible within the entire range of operating temperatures.

max

It is known to use for the n-type leg of Peltier couples an alloy constituted by a mix-crystal of the system Bi Te -Bi Se The alloy of 80 mole percent Bi Te and 20 mole percent Bi Se with a suitable doping substance has been considered particularly Well suitable because of its minimal lattice thermal conductance. The efiectivity of this allow at room temperature (20 C.) is

It is an object of my invention to further improve ntype semiconductors, particularly those for Peltier couples, with respect to their thermoelectric properties.

According to my invention, a thermoelectric semiconductor member of n-type conductance is formed of an alloy of the system Bi Te -Bi Se -As Se having a percentile molecular composition of the components within the range from 2.0 mole percent Bi Se 2.0 mole percent As Se and 96 mole percent Bi Te to 15.0 mole percent Bi Se 5.0 mole percent As Se and 80 mole percent Bi Te the semiconductor member being doped for thermoelectric effectivity with halogen or metal halogenide.

Preferably employed as halogen dopant is chlorine, although I and Br are likewise well suitable. used as a metal halogenide is copper bromide (CuBr).

I have discovered that within the above-stated range of composition the halogen doping not only secures high eifectivity at room temperature (20 C.), but also higher maximal temperature differences in the working temperature range from +40 C. downward than obtained with the alloy of 80 mole percent Bi Te -20 mole percent Preferably 3,310,493 Patented Mar. 21, 1967 Bi Se heretofore considered to afford optimal thermoelectric properties.

Relative to Bi Te alloys that contain As Se exclusively, the doped ternary alloy according to the invention has the further advantage of readily lending itself to the production of homogeneous material and avoidance of irregularly crystallized regions by application of the normal freezing method.

Semiconductor members of n-type conductance according to the invention are applicable, together with suitable p-type members, in couples for cooling purposes. The data for the maximal attainable temperature reduction AT stated in the following Table 1, were measured with three different semiconductor members according to the invention in combination with mix-crystal p-type leg composed of 20 mole percent Sb Te and 30 mole percent Bi Te having an effectivity of z=2.0 10- C. at 25 C.

TABLE 1 Semiconductor: AT C.] I 65 II 76 HI The temperature of the hot junctions in all cases was +40 C.

The semiconductor members I, II and III were composed as follows:

Semiconductor I:

96 mole percent Bi Te 2 mole percent Bi Se 2 mole percent As Se +0.05 weight-percent CuBr Semiconductor II:

88 mole percent Bi Te 10 mole percent Bi Se 2 mole percent As Se +0.04 weight-percent Cl Semiconductor III:

mole percent Bi Te 10 mole percent Bi Se 5 mole percent As Se +0.05 weight-percent CuBr The following Table 2 indicates the thermoelectric properties of the semiconductor member II:

TABLE 2 Thermoforce, aLuV/degree] Electric conductance, a 9- cm. 1282 Thermal conductance, k-10+ [W/cm.-degree] 1.4 Thermoelectric etfectivity, z-10 [degree 3.1

TABLE 3 Semiconductor Te [2'] Bi Sb [2'] Se [g] I 23. 7050 8. 1747 12. 8763 0. 2439 I1 29. 1149 7. 4274 12. 9813 O. 4762 III 29. 5311 5. 8531 13, 6393 0. 9259 The mix-crystal semiconductors according to the invention were produced by the preferred method described presently. The above-described quantities of the constituents for each semiconductor were first melted together in an evacuated quartz tube at 800 (1., thus producing a prealloy. Thereafter the prealloy was subjected to cooling and solidification by the normal freezing method. That is, the melt, contained in an elongated crucible or boat, was caused to gradually freeze from one end to the other. The normal freezing was performed at a temperature of about 800 C. at a rate of about 0.6 cm./h. The normal freezing step can also be performed by the known zone melting method. In this manner, excellent products, exhibiting the above-described qualities are obtained'.

The accompanying drawing shows by way of example a Peltier pile containing semiconductor legs according to the invention. The pile is composed of p-type legs 1 of prismatic shape consisting of a mix-crystal with tellurium n-type legs 2 of prismatic shape. The n-type legs 2 consist of a ternary mix-crystal of Bi Te -Bi Se -As Se doped with halogen according to the invention as described above. The alternately p-type and n-type legs are spaced from each other, and each two adjacent ones are electrically interconnected by bridge pieces 3 or 4 of copper. The pile may comprise more pairs of legs than illustrated, and several rows of legs may be composed to form a battery or block. All legs of the pile are electrically connected in series. When current passes through the pile, all hot junctions are located on one and the same side, for example the side of bridge pieces 4 and all cold junctions on the side of the other bridge pieces. The bridge pieces may be joined with heat-exchanging or heat-dissipating fins or other devices for transmitting or supplying heat, depending upon the particular use to be made of the device.

The p-type legs 1 of Peltier couples according to the invention may consist of the above-mentioned Sb Te -Bi Te mixed crystals composed of 70 mole percent Sb Te and 30 mole percent Bi Te However, any other suitable p-type thermoelectric materials may be used. Particularly favorable results are obtained when using p-type legs according to my copending application Ser. N 0. 277,617, filed concurrently herewith now abandoned, which consist of a mixed crystal of bismuth telluride and antimony telluride within the range of 73 to 80 mole percent Sb Te and 20 to 27 mole percent Bi Te and which contain an excess of tellurium above stoichiometry in an amount of 2 to 8% relative to the weight of the total composition and also 'a selenium addition of 0.5 to preferably not more than 3%, by Weight of the total composition. This p-type thermoelectric semiconductor composition can be produced by the same method as the one described above with reference to the n-type doped ternary composition, namely by melting the above-mentioned components of the p-type material in an evacuated quartz tube at 800 C., and then subjecting the melt to normal freezing from a temperature of about 800 C. at a rate of approximately 0.6 cm. per hour either by cooling the melt progressively from one end of the crucible to the other or by applying the zone-melting method.

I claim:

1. A thermoelectric semiconductor member of n-type conductance consisting of an alloy of the system Bi Te Bi Se -As Se in a percentile molecular composition within the range from 2.0 mole percent Bi Se 2.0 mole percent As Se and 96 mole percent Bi Te to 15.0 mole percent Bi Se 5 .0 mole percent As Se and mole percent Bi Te said member being doped for thermoelectric effectivity with 0.01 to 0.1% by weight of substance from the group consisting of halogens and copper bromide.

2. A thermoelectric semiconductor member of n-type conductance consisting of a Bi Te -Bi Se -As Se alloy in the range from 2.0 mole percent Bi Se 2.0 mole percent As Se and 96 mole percent Bi Te to 15.0 mole percent Bi Se 5.0 mole percent A-s Se and 80 mole percent Bi Te said member being doped with 0.01 to 0.1 weightpercent of halogen.

3. A thermoelectric semiconductor member of n-type conductance consisting of a Bi Te -Bi Se -As Se alloy in the range from 2.0 mole percent Bi Se 2.0 mole percent As Se and 96 mole percent Bi Te to 15.0 mole percent Bi Se 5.0 mole percent As Se and 80 mole percent Bi Te said member being doped with copper bromide (C'uBr) in an amount of 0.03 to 0.06% by weight.

4. The method of producing a thermoelectric semiconductor member of n-type conductance, which comprises preparing in vacuum at about 800 C. a molten pre-alloy of Bi Te -Bi Se -As Se in the range from 2.0 mole percent Bi Se 2.0 mole percent As Se and 96 mole percent Bi Te to 15.0 percent Bi Se 5.0 mole percent As Se and 80 mole percent Bi Te with an addition of 0.01 to 0.1% by weight of substance from the group consisting of halogens and copper bromide, and subjecting the melt to normal freezing from a temperature of about 750 C. at a rate of about 0.6 cm. per hour.

References Cited by the Examiner Egli: Thermoelectricity, John Wiley and Sons, 1960, pages 136l45.

Gordiakova et al.: Investigation of Thermoelectric Properties of Solid Solutions Bi Te -Bi Se Soviet Physics, volume 3, No. 1, January 1958, pages 1-14.

Sinani et al., Solid Solutions of Bi Te -Bi Se as Materials for Thermoelements-Zhurnal Tekhm'cheskoy Fiziki, volume XXVI, No. 10, pages 23982399 (1956).

Selenium and Tellurium Abstractsvolume 3, No. 5, May 1962, Battelle Memorial Institute, page 635, Ahstract No. 1109.

TOBIAS E. LEVOW, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

R. D. EDMONDS, Assistant Examiner. 

1. A THERMOELECTRIC SEMICONDUCTOR MEMEBER OF N-TYPE CONDUCTANCE CONSISTING OF AN ALLOY OF THE SYSTEM BI2TE3BI2-SE3-AS2SE3 IN A PERCENTILE MOLECULAR COMPOSITION WITHIN THE RANGE FROM 2.0 MOLE PERCENT BI2SE3, 2.0 MOLE PERCENT AS2SE3 AND 96 MOLE PERCENT BI2TE3 TO 15.0 MOLE PERCENT BI2SE3, 5.0 MOLE PERCENT AS2SE3 AND 80 MOLE PERCENT BI2TE3, SAID MEMBER BEING DOPED FOR THERMOELECTRIC EFFECTIVITY WITH 0.01 TO 0.1% BY WEIGHT OF SUBSTANCE FROM THE GROUP CONSISTING OF HALOGENS AND COPPER BROMIDE. 